This invention relates generally to electrical terminal assemblies of the type wherein a pair of conductor wires are clamped by a screw activated pressure plate causing an electrical connection to be formed therebetween.
The invention is more particularly directed to a terminal clamp assembly which is capable of accepting conductor wires of dissimilar diameters and insuring that a firm and reliable clamping pressure is maintained on the pair of wires.
Certain prior art devices have been designed to incorporate a washer-type plate preassembled on a screw fastener so that the plate will clampingly engage a pair of conductor wires bringing them into electrical contact with one another. These prior art devices typically incorporate a rib structure at the undersurface of the washer to concentrate the clamping pressure on the conductor wires in an effort to insure a firm electrical contact. Such prior art devices still tend to be somewhat unreliable in that they utilize a single rib or, at most, two ribs contacting a given conductor wire. Excessive vibrations and/or external forces applied to the conductor wires may therefore tend to relax the clamping pressure on the conductors and create an unreliable electrical joint. Furthermore, the ribs in the prior art devices concentrate the clamping forces at a discrete region of the conductor to the extent that the clamping force could, in combination with vibrations and external loads, cause the conductor wire to be severed or excessively deformed.
Other prior art devices of this general type have been developed in an effort to insure the adaptability of the devices to accept a pair of conductor wires of different diameters. Tiltability of a clamping plate has, in certain prior art devices, been achieved by a particularly designed clamping surface beneath the head of a screw. For example, U.S. Pat. Nos. 3,744,012 and 3,891,296 show terminal clamps in which the tiltability is facilitated by a recess in the clamping surface of the head of a screw.
It is therefore an object of this invention to provide a terminal clamp assembly with a capability to accommodate and firmly clamp a pair of wires either of the same or of different diameters.
A further object of the invention is to provide a terminal clamp assembly having a washer-like plate with a clamping surface configured to distribute a clamping load on a plurality of discrete regions on a given conductor wire while also simultaneously applying lateral forces to the conductor wire in opposing directions.
A still further object of the invention is to provide a terminal clamp assembly in which the clamping pressure is reliably applied in a region directly adjacent the aperture of a clamping washer.
The above and other objects are achieved by a clamp assembly comprising a screw-type fastener with a generally planar polygonal-shaped washer-type clamping plate preassembled to the fastener and directly adjacent the head of the fastener. The clamping plate includes a plurality of generally radially directed ribs formed on the undersurface. The plurality of ribs comprises two sets of alternately disposed ribs. The ribs of a first set extend from the corners of the washer plate inwardly and the ribs of a second set extend from the sides of the washer plate inwardly. The ribs of the first set are formed to taper inwardly with their maximum thickness adjacent the outer periphery of the washer while the ribs of the second set are formed to taper outwardly with their maximum thickness adjacent the aperture of the washer. This configuration causes the conductor wire to be subjected to laterally directed forces in addition to clamping forces and tends to deform the conductor wire into a serpentine configuration beneath the clamping plate which enhances the capability of the wires to resist unauthorized forces axially of the conductors.
The clamping plate is further uniquely configured to include a short tubular projection directly adjacent the aperture to insure that the clamping forces are applied near the aperture rather than outwardly of the aperture. Such a structure therefore permits the plate to tilt without interference from the clamping surface of the head. Other features of the invention that contribute to its efficient operation include a reduction in the thickness of the washer at the walls of the aperture. Since the aperture size should be minimized if the washer is to be retained by conventional preassembly techniques, the axial extent of the aperture walls becomes a limiting factor in the degree of tiltability of the washer .